1. Field
Embodiments of the present invention relate to a solenoid valve for a brake system, and more particularly, a solenoid valve for a brake system capable of increasing a brake hydraulic pressure supplied to a wheel cylinder during general braking and improving durability thereof by increasing compression strength thereof.
2. Description of the Related Art
Hydraulic brake systems should be installed for braking in vehicles, and recently, various types of systems have been proposed for obtaining more powerful and stable braking forces. As an example of the hydraulic brake systems, there are an anti-lock brake system (ABS) which prevents wheels from slipping during breaking, a brake traction control system (BTCS) which prevents driving wheels from slipping when vehicles are suddenly or rapidly accelerated, and a vehicle attitude control system (e.g., electronic stability control (ESC)) which combines the ABS and the BTCS to control brake hydraulic pressure and maintains a stable state for vehicle driving.
As shown in FIG. 1, a hydraulic brake system includes a master cylinder 10 configured to generate pressure needed for braking, a plurality of solenoid valves 30, 40, 50 and 60 configured to control hydraulic pressure for braking that is transferred to wheel cylinders 20 installed on each of wheels FL, FR, RL, and RR of a vehicle, low pressure accumulators 70 configured to temporarily store oil, pumps 80 and a motor 85 configured to forcibly pump the oil temporarily stored in the low pressure accumulators 70, orifices 90 configured to reduce pressure pulses of the oil pumped from the pump 80, an electronic control unit (ECU, not shown) configured to electrically control the solenoid valves 30, 40, 50, and 60 and to drive the pumps 80. In addition, the solenoid valves 30, 40, 50, and 60, the low pressure accumulators 70, the pumps 80, and the like are compactly installed in a modulator block 100 made of an aluminum based material, and the ECU including a coil assembly (not shown) of each of the solenoid valves 30, 40, 50, and 60 and an ECU housing (not shown) having embedded circuit boards is coupled to the modulator block 100.
The hydraulic brake system described above selects a ABS, TCS, or ESC mode according to a driving state of a vehicle to perform an appropriate braking and stable braking operation.
Meanwhile, the plurality of solenoid valves 30, 40, 50, and 60 provided in a brake system configured to control a braking pressure are divided into a normal open (NO) type solenoid valve which usually maintains in an open state and a normal close (NC) type solenoid valve which usually maintains in a close state. At this time, NO type traction control (TC) valves 30 first connected to ports of the master cylinder 10 through flow paths usually maintains in an open state, and when road surface slip occurs due to sudden unintended starting of a vehicle or the like, the traction control (TC) valves 30 close a flow path to transfer a braking pressure generated by the pump 80 to wheel cylinders of a vehicle, and thus braking of a vehicle may be performed even when a driver does not step on a brake pedal. The TC valve 30 transfers hydraulic pressure flowing from the master cylinder 10 to the wheel cylinders 20 through the TC valves 30 passing through the NO type inlet valves 50 provided on an up stream of each of the wheel cylinders 20. That is, the TC valve 30 usually maintains in an open state, and transfers brake hydraulic pressure generated from the master cylinder 10 toward the wheel cylinders 20 during general braking (e.g., a combined break system (CBS)) by a brake pedal.
FIG. 2 shows a conventional normal open type solenoid valve (TC valve). The TC valve 30 includes a magnet core 31 having a through hole 31a in a longitudinal direction in a center thereof and a flow path 31b on an circumference thereof, a dome-shaped sleeve 32 installed on the magnet core 31 and closing an upper part of the magnet core 31, a valve seat 33 installed in the magnet core 31, an armature 34 and a plunger 35 installed in the upper part of the magnet core 31 and the through hole 31a and configured to move forward and backward, and a filter member 36 installed on a lower part of the magnet core 31. At this time, a separate bypass flow path 36a is formed in the filter member 36 so that oil flows into an outlet path 103 through an inlet path 102 of a modulator block 100, and a check valve 37 is provided in the bypass flow path 36a. 
The TC valve 30 is installed in the modulator block 100 and a flow path of oil flowing through the inlet path 102 is divided into two flow paths when the oil passes through the TC valve 30. That is, oil flowing through the inlet path 102 located on an side of the TC valve 30 is filtered by the filter member 36, transferred to the outlet path 103 through the through hole 31a and a flow path 31b formed on an circumference of the magnet core 31, and transferred to the outlet path 103 through the bypass flow path 36a formed in the filter member 36. At this time, an amount of oil flowing through the bypass flow path 36a has 80% of a total amount of oil passing through the TC valve 30.
Meanwhile, as shown in FIG. 1, according to hydraulic pressure generated from the master cylinder 10 is transferred to two wheel cylinders 20 through one TC valve 30, a TC valve 30 structure is improved and provided so as to secure a sufficient amount of oil during general braking (CBS). For example, as shown in FIG. 2, a structure in which a lower part of the magnet core 31 coupled to the filter member 36 is coupled to the filter member 36 with an interval is used so that a rate of an amount of oil flowing into the bypass flow path 36a is increased. Although an amount of oil transferred to the wheel cylinders 20 may be increased by the structure during general braking, a coupling force of the magnet core 31 and the filter member is decreased, and thus there are problems in that compression strength and durability thereof are degraded.
In addition, according to trends miniaturizing products, since overall heights of solenoid valves are decreased and areas passing through bypass flow paths 36a are decreased, a sufficient amount of oil is not supplied compared to existing systems, and there is problem in that the performance of valves and brake systems is degraded.